The STMicroelectronics SM30T21AY is a unidirectional TRANSIL™ TVS diode from the automotive SM30TY series, rated for 3000 W peak pulse power (10/1000 µs waveform) with a clamping voltage of 29.2 V at 102.7 A peak pulse current. This surge rating is sized for automotive load-dump and inductive-load transients on 12 V and 24 V vehicle electrical systems — the 18 V reverse standoff voltage sits comfortably above the nominal rail, so it does not conduct during normal operation, but the 20 V minimum breakdown ensures it triggers before the downstream electronics see damaging overvoltage.
AEC-Q101 and the full temperature range
The 175°C TJ(max) rating means the die can handle self-heating from repetitive surge events without derating prematurely — a common failure point for commercial-grade TVS diodes in a hot environment.
For dual-sourcing or second-source qualification, the SM30TY series includes functionally similar variants at other voltage ratings; the base product number SM30T21 identifies the 18 V standoff / 20 V breakdown tier within the family. If the application needs a different clamp voltage, the same footprint and qualification level are available across the SM30TY range.